In prior U.S. Pat. Nos. 3,062,167, 3,399,643 and 3,628,847 there are disclosed and claimed trim attachments for power boats which comprise trim members or tabs that are hinged to the stern of the boat and are actuated to varying angles to provide control of the attitude of the boat. In U.S. Pat. No. 3,628,487 there is disclosed a hydraulically operated trim attachment comprising a trim tab indicator system comprising a pair of trim members hinged to the stern of a boat, one of each side of the center line of the boat and a hydraulic cylinder individual to each trim member having a head at one end and a head at the other end, and a tubular shaft connected to the piston and extending through the other end of the cylinder. A bracket is connected to the first head and has a surface complementary to the transom of the boat and is mounted on the transom.
It is desirable to be able to indicate continuously the position of the trim tabs.
It has heretofore been suggested that the position of trim tabs can be sensed by providing pickups on the shaft of an electrically motor driven trim tab as shown in U.S. Pat. No. 4,232,626. U.S. Pat. No. 3,641,965 shows a arrangement utilized with stern drives to provide a signal proportional to the angle of tilt of the stern drive. U.S. Pat. No. 4,420,741 shows an electronic position monitor and readout device for trim tabs on boats which functions on the basis of timing the travel of the trim tabs to determine the position.
U.S. Pat. No. 3,160,836 shows cylinders with external position sensors and U.S. Pat. No. 3,654,549 and British Patent No. 1,088,544 (1967) show cylinders with internal devices.
Each of these systems are complex and difficult to make.
Among the objects of the present invention are to provide a trim tab indicator system which is compact; easy to manufacture; is readily adapted to cylinders already in use and which continuously provides a signal indicative of the position of the trim tab.
In accordance with the invention, a tubular coil is fixed on the first head and extends axially within the cylinder, and a floating rod of magnetically permeable material is provided in the tubular shaft with a lower end engaging the base of the tubular opening of the shaft with its upper end extending into the coil such that movement of the trim tab changes the inductive relationship between the rod and the coil to provide a signal representing the position of the tab.